1. The Field of the Invention
The present invention relates to a method and apparatus to be located upstream of any flow-splitting device for proportioning the mass rates of the non-predominant (volumetric-wise) component in a two phase mixture flowing in a pipe.
2. The Prior Art
The present invention will be discussed with reference to a preferred use in the field of petroleum production and, in particular, to steam distribution networks for steam injection during enhanced oil recovery operations. During such operations the proportion of the gas phase mass of the steam to the total mass of the steam, commonly known as the steam quality, needs to be controlled throughout the steam distribution network at the surface in order to minimize the phenomenon known as "phase splitting" which occurs at substantially all nodes in a pipe network where the two-phase fluid flow is split into two or more branches and the gas phase mass extraction ratios of the branches are not necessarily equal.
This phase splitting problem causes the quality of the steam (i.e. the ratio of the gas phase mass to total mass of the steam) to be other than that desired and/or required at each final destination or injection point. This, in turn, causes the total heat input at the final destination subsurface strata to be out of specification or tolerance resulting in an inefficient or poor steam sweep of the layer. Unless there is a perfectly symmetrical gas phase mass rate distribution (equal gas or predominant phase extraction ratios) at each and every junction in the steam distribution system and a very specific geometry of the piping system, each flow-splitting device in the system (usually a T-junction) will cause the phase-splitting problem to become more severe by increasing the difference in the liquid mass (or non-predominant phase) extraction ratios as the steam passes through each successive junction. Since it is not always practical to have the same gas phase mass extraction rates at every node of a network, it becomes highly desirable to have a device to fix or minimize this phase-splitting problem, at least at those junctions where it will have the most significant effect.
Currently there are several alternative approaches to correcting or minimizing the above discussed problem, including the use of the following described devices. There are a number of different configurations of static mixers each of which is used to homogenize a two-phase fluid flow and covert it into a mist just upstream of the flow-splitting device (for example a T-junction) by dispersing the liquid phase within the gas phase. Examples of these devices can be found in U.S. Pat. Nos. 3,599,943; 3,785,620; and 4,062,524.
A carburetor type of approach has also been proposed. This type of device has a chamber to trap the liquid phase upstream of the phase-splitting device (again a T-junction) and one or more tubes connecting liquid chamber to either immediately before the junction (via a single tube) or to the exit of each branch thereof (via two tubes). The passage of the gaseous phase over the end of the respective tubes will create suction drawing the liquid phase from the liquid chamber into junction device or the branch ends thereof in proportion to the vapor mass rate flowing in each branch leg of the junction. These types of devices are shown in U.S. Pat. No. 5,218,985, for the single tube embodiment, and U.S. patent application Ser. No. 07/961,977 filed Oct. 16, 1992, for the dual tube embodiment.
There are also a number of devices having a member which either fixedly or adjustably extends into a flow stream to provide a variable cross section area within the pipe. This member generally acts on the fluid flow just upstream of the flow-splitting device by one of two different methods. In one method the perimeter of the pipe is affected by means of a movable internal partition to thereby control the steam quality at two separated outlets, essentially based on wet perimeter considerations. In the other method the cross sectional area of the pipe is affected by means of at least one plate mounted within the pipe facing generally perpendicular to the flow stream and located upstream of a fixed internal partition that isolates the two outlets of the junction. The steam quality at the two outlets is control by rotating the plate to adjust effective cross-sectional area of the pipe upstream of the two outlets. Examples of these devices can be found in U.S. Pat. Nos. 2,114,653; 3,080,884; 4,269,211; 4,354,528; 4,824,614; and 5,165,450.